Compound bows are commonly used for hunting and for sport. Compound bows rely on one or more cams or pulleys which are used to supply a mechanical advantage when the bow is drawn and released. Tension of the bowstring is increased by the archer as the archer pulls the bowstring back in order to fire an arrow. Cams and pulleys decrease the amount of force which the archer must input in order to fire an arrow by effectively transferring the tension force to a propellant force on the arrow.
Accordingly, there is a present need for a cam that is capable of expanding to maximize the amount of contact it has with the bowstring and, in turn, the amount of tension that the bowstring experiences. The present invention is a bow cam that expands as the string is drawn and locks into place at full draw. Intermittently increasing the radius of a cam as the bowstring is pulled back would increase the distance which bowstring needs to travel to return to rest. As a result, the archer experiences no added resistance when drawing back the bow, but the bowstring experiences an increased tension as the bowstring retracts to the resting position, which translates to an increase of the expelling force on the arrow.